Implantable Medical Device with a Voltage Protection Circuit

ABSTRACT

An implantable medical device has a hermetically sealed housing with at least one feedthrough therein for a conductive path between an RF antenna carried by the housing, and an RF telemetry circuit contained in the housing. The feedthrough has a feedthrough housing with a capacitor element therein having first and second capacitor plate configurations, with a first of the capacitor plate configurations being connected to the RF antenna and a second of the capacitor plate configurations being connected to the RF telemetry circuit. The feedthrough functions both as a hermetic seal and as a galvanic isolation for voltage protection of the components of the RF telemetry circuit, and other circuitry in the sealed housing connected thereto.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention generally relates to implantable medical devicessuch as implantable cardiac pacemakers and implantablecardioverter/defibrillators, and in particular to a capacitivefeedthrough for filtering off external interference signals, e.g.defibrillation signals, in order to protect the electronic circuits andtelemetry circuits of such an implanted device.

2. Description of the Prior Art

Implantable medical devices, including cardiac rhythm management devicessuch as pacemakers and implantable cardioverter/defibrillators,typically have the capability to communicate data with an externalprogrammer via a radiofrequency telemetry link. A clinician may use suchan external programmer to program the operating parameters of animplanted medical device. For example, the pacing and other operatingcharacteristics of a pacemaker are typically modified after implantationin this manner. Modern implantable devices also include the capabilityfor bidirectional communication so that information can be transmittedto the programmer from the implanted device. Among the data which maytypically be telemetered from an implantable device are variousoperating parameters and physiological data. The implantable devicegenerates and receives the radio signals by means of an antenna. Today,antennas capable of far-field communications are of increasing interestin implantable medical devices, which allows communication over muchgreater distances than inductively coupled antennas.

The technology of cardiac pacemakers has developed in sophistication andfunctionality over the years. In general, cardiac pacemakers aredesigned to control the heart by correcting or compensating for variousheart abnormalities which can be encountered in human patients. Forexample, cardiac pacemakers may provide therapeutic stimulation to theheart by delivering therapeutic pulses such as pacing, cardioversion ordefibrillation pulses. However, with this increasing sophistication hascome a concomitant increase in sensitivity of the implantable devices tomisoperation due to external influences such as defibrillation,electrocautery, and the like. Such interference or voltage pulses may bereceived by the antenna, for example, at locations where galvanicexposure against tissue occurs and may be conducted further into theelectronic circuits and RF telemetry circuits of the medical device.This may cause the medical device to falsely identify the interferenceas being of cardiac origin and give rise to, for example, an erroneousoutput rate, or in worst case, it may change the state of or destroycomponents of the circuits, which, in turn, may severely damage thefunctions of the medical device.

Conventional implantable devices, such as cardiac pacemakers andimplantable cardioverter/defibrillators, are therefore generallyprovided with protection circuits or filter circuits adapted to protectthe electronic circuits and RF telemetry circuits of the medical deviceagainst undesired voltage pulses, i.e. to filter off external voltagetransients or pulses. Conventionally, a capacitance is arranged withinthe device and connected in series with the antenna and the electroniccircuits and RF telemetry circuits as protection circuit or filtercircuit adapted to filter off external interference signals such asdefibrillation signals. Thus, RF signals are transferred via the antennalead through the galvanically conductive feedthrough passing through theserial capacitor while external interference signals are filtered off.

However, this conventional solution is impaired with a number ofdrawbacks. For example, the filter circuit, i.e. the capacitor, requiresextra space, which may be a problem in implantable devices, such ascardiac pacemakers, where internal space is limited. Moreover, since theexternal interference signals are transferred into the hermeticallysealed device, they may give rise to interference leakage within thedevice.

Hence, there is a need for an improved circuit that in an effective waycan protect the internal circuits of an implanted medical device againstundesired voltage pulses caused by exposure to e.g. defibrillationand/or electrocautery.

SUMMARY OF THE INVENTION

Thus, an object of the present invention is to provide an improvedprotection circuit that can effectively protect the internal circuits ofan implanted medical device against undesired voltage pulses caused byexposure to defibrillation and/or electrocautery received by theantenna, for example, at galvanic exposure against tissue and beconducted further into the electronic circuits and RF telemetry circuitsof the medical device.

Another object of the present invention is to provide such a protectioncircuit that can be implemented in an implanted medical device in aspace efficient manner.

A further object of the present invention is to provide such aprotection circuit that can be implemented in an implanted medicaldevice in a cost efficient manner.

According to an aspect of the present invention, there is provided animplantable medical device including a hermetically sealed housinghaving at least one feedthrough arranged for at least one RF telemetryantenna. The medical device has at least one RF telemetry circuit havingan RF transmitter and receiver connected to the antenna; at least onecontroller circuit adapted to output and receive data contained in amodulated carrier generated or received, via the antenna, by the RFtelemetry circuitry; wherein the feedthrough has a feedthrough housingand a capacitor element arranged in the feedthrough housing, the elementbeing connected in series between the RF telemetry circuit and theantenna and including at least one first capacitor plate being connectedto the antenna and at least one second capacitor plate being connectedto the RF telemetry circuit, the capacitor element being adapted towithstand the voltage amplitude of a pulse capable of modifying state ofor destroying at least one component of the RF telemetry circuit or theelectronic circuit.

Thus, the invention is based on the idea of arranging the feedthroughfor the antenna as a filter circuit serving the dual purposes offunctioning as a hermetic seal and a galvanic insulation circuit forblocking voltage transients or pulses, due to exposure to defibrillationand/or electrocautery conducted into the device due to galvanic contactbetween the RF circuits of the device and tissue via an antenna externalto the housing in tissue contact and capable of modifying state of ordestroying at least one component of the RF telemetry circuit or theelectronic circuit, from reaching the components. Accordingly, the needof a separate galvanically conducting feedthrough is removed.

This solution provides several advantages over the conventionaltechnique. One advantage is that, since the filter circuit, i.e. thecapacitor element, is integrated in the antenna feedthrough, valuablespace in the medical device can be saved. Another advantage is that therisk of possible interference leakage into the hermetically sealeddevice can be significantly reduced due to the fact that the filtercircuit, i.e. the capacitor, is arranged in the feedthrough and, thus,prevents the external voltage transients or pulses from entering intothe medical device. Furthermore, combining two functions, i.e. thehermetic seal and the galvanic isolation, in the feedthrough entailscost savings, which also is an advantage in comparison with the knowntechnique.

Preferably, the at least one first capacitor plate is facing outwardsfrom the device and is being made of a bio compatible material, forexample, titanium, platinum, or alumina.

In a further embodiment of the present invention, the at least one firstcapacitor plate comprises a first set of capacitor plates beinginterconnected to each other and the at least one second capacitor platecomprises a second set of capacitor plates being interconnected to each,wherein plates from the first set are alternated with plates from thesecond set and adjacent plates are separated with an isolatingdielectric material.

In an embodiment of the present invention, the feedthrough housing has asubstantially cylindrical shape and the plates of the first set ofcapacitor plates and the second set of capacitor plates aresubstantially circular and are arranged substantially coaxially in thefeedthrough housing. According to this embodiment, the plates of thefirst and second set of capacitor plates are arranged substantiallyparallel with each other and thus forming a pile- or stack-likeconfiguration.

In a further embodiment of the present invention, intermediate plates ofthe first set of capacitor plates and intermediate plates of the secondset of capacitor plates are provided with via holes, the first set ofintermediate capacitor plates being coupled to each other by means ofleads arranged through the via holes of the plates of the second set,and the second set of intermediate capacitor plates being coupled toeach other by means of leads arranged through the via holes of theplates of the first set.

In accordance with yet another embodiment of the present invention, afirst connecting element is connected to the antenna and a secondconnecting element is connected to the RF telemetry circuit, wherein theplates of the first and second set of capacitor plates are connected tothe first connecting element and to the second connecting element,respectively, and wherein the plates of the first and second set ofcapacitor plates are arranged substantially perpendicular to the firstand second connecting element, respectively.

Preferably, the feedthrough housing has a substantially cylindricalshape and the capacitor plates of the first set of intermediatecapacitor plates and the second set of intermediate capacitor plates aresubstantially rectangular, each plate having a width being substantiallyequal to an inner width of a longitudinal cross-section of thesubstantially cylindrically shaped feedthrough housing. Accordingly, thewidths of adjacent plates will vary depending on the inner width of thefeedthrough housing at the specific location of the plate.

In still another embodiment of the present invention, the plates offirst and second set of intermediate capacitor plates are arranged assubstantially concentric cylinders.

According to an embodiment of the present invention, the capacitorelement is adapted to function as an antenna matching element.

Conveniently, the capacitor element according to the present inventionis dimensioned to withstand a voltage exceeding 100 V.

BRIEF DESCRIPTION OF THE DRAWINGS

The features that characterize the invention, both as to organizationand to method of operation, together with further objects and advantagesthereof, will be better understood from the following description usedin conjunction with the accompanying drawings. It is to be expresslyunderstood that the drawings is for the purpose of illustration anddescription and is not intended as a definition of the limits of theinvention. These and other objects attained, and advantages offered, bythe present invention will become more fully apparent as the descriptionthat now follows is read in conjunction with the accompanying drawings.

FIG. 1 diagrammatically shows an implantable medical device comprising acapacitive feedthrough for protecting the electronic circuitry of thedevice against undesired voltage pulses caused by exposure todefibrillation and/or electrocautery conducted into the device due togalvanic contact between the RF circuits of the device and tissue via anantenna or apart of the medical device capable of functioning as anantenna being in tissue contact and connected to electronic circuitry ofthe device in accordance with the general principles of the presentinvention[[;]].

FIG. 2 diagrammatically shows a cross-sectional view of an embodiment ofthe feedthrough according to the present invention.

FIG. 3 is a diagrammatic perspective view of the feedthrough shown inFIG. 2.

FIG. 4 diagrammatically shows a cross-sectional view of anotherembodiment of the feedthrough according to the present invention.

FIG. 5 is a diagrammatic perspective view of the feedthrough shown inFIG. 4.

FIG. 6 is a cross-sectional view in plane parallel with the line A-A inFIG. 4 and perpendicular to the view in FIG. 4.

FIG. 7 is a cross-sectional view the plane parallel with the line A-A inFIG. 4 and perpendicular to the view in FIG. 4 of an alternativeembodiment to the embodiment shown in FIG. 6.

FIG. 8 diagrammatically shows a cross-sectional view of yet anotherembodiment of the feedthrough according to the present invention.

FIG. 9 is a cross-sectional view in plane parallel with the line A-A inFIG. 8 and perpendicular to the view in FIG. 8.

FIG. 10 diagrammatically shows a cross-sectional view of still anotherembodiment of the feedthrough according to the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

With reference first to FIG. 1, an implantable medical device (IMD) 100having a serial capacitive feedthrough adapted to protect the electroniccircuitry of the device against undesired voltage transients caused byexposure to defibrillation and/or electrocautery conducted into thedevice via an antenna or a part of the medical device capable offunctioning as an antenna being in tissue contact and connected toelectronic circuitry of the device in accordance with the presentinvention will be described.

The IMD 100 is provided with an antenna 102 for communication withexternal devices such as an external programmer. Preferably, the antenna102 is suitable for radiating and receiving far-field electromagneticradiation. It should be noted that the housing effectively is a part ofthe antenna and affects the radiation properties of the antenna 102. Thehousing is further in contact with the tissue. The IMD 100 includes ahermetically sealed housing 103 provided with an antenna feedthrough 104through which the antenna 102 is located and feedthroughs for medicalleads, which housing 103 typically is formed of a biocompatible metal,e.g. titanium. The housing 103 contains a therapy circuitry 105 forproviding particular functionality to the device such as cardiac rhythmmanagement, or neuromuscular stimulation, RF telemetry circuitry 106 forproviding RF communications. A battery (not shown) supplies power to theelectronic circuitry within the housing 103. One or more leads 107 areconnected to the therapy circuitry 105, which lead or leads 107 may beunipolar or bipolar, and may be adapted to operate in cooperation with awide variety of implantable medical devices. Moreover, the lead or theleads 107 may include any of the passive or active fixation mechanismsknown in the art for fixation of the lead 107 to the cardiac tissue whenfinal position has been found. As an example, lead distal tip (notshown) may include a tined tip or a fixation helix. The leads 107 alsocarry one or more electrodes, such as a tip electrode or a ringelectrode. The electrode senses electrical signals associated withdepolarization and repolarization of the heart. In addition, theelectrode may also transmit pacing pulses for causing depolarization ofcardiac tissue adjacent to the electrode. Furthermore, the leads 107also comprise sensing means arranged to sense signals related heartactivity.

A microprocessor controller 110 controls the operation of the therapycircuit 105, which includes sensing and stimulus generation circuitrythat are connected to the electrodes of the lead or leads 107 forcontrol of heart rhythm, and the RF telemetry circuitry for transmittingand receiving a carrier signal at a specific frequency modulated withtelemetry data.

The controller 110 also outputs and receives the data contained in themodulated carrier generated or received by the RF telemetry circuitry106. The RF telemetry circuitry 106 comprises an RF transmitter andreceiver that are connected to the antenna 102.

The capacitive feedthrough includes an antenna feedthrough housing 104and a capacitor element 108 connected in series with the antenna 102 andis arranged to withstand a voltage amplitude of a pulse received by theantenna 102 and capable of modifying the state of or destroyingcomponents of the RF telemetry circuitry 106, the controller 110, or thetherapy circuit 105. Preferably, the capacitor element is dimensioned towithstand a voltage exceeding 100 V, and, more preferably, to withstanda voltage in the range of 75-1000 V.

The capacitor element 108 can also be adapted to function as a matchingcircuit to adjust the impedance of the antenna 102 to the impedance ofthe RF telemetry circuitry 106. The capacitor element loads the antenna102 with an amount of capacitance to thereby adjust the effectiveelectrical length of the antenna, and hence the resonance frequency ofthe antenna. By matching the antenna impedance to the impedance of theRF telemetry circuitry at a specific carrier frequency, the reactance ofthe antenna may be tuned out at that frequency so that the antenna formsa resonant structure and efficiently transmits/receives far-fieldradiation.

According to the general principles of the present invention, thecapacitor element 108 includes at least one first capacitor plate 112and at least one second capacitor plate 114. A cavity 109 defined by thefeedthrough housing 104, the at least one first capacitor plate 112 andthe at least one second capacitor plate 114 is filled with an isolatingdielectric material. According to embodiments of the present invention,the dielectric material is hermetic, essentially free of pores anddiffusion proof in order to function as a feedthrough material.Moreover, the dielectric material is an electrically insulating materialwith low losses, i.e. a high Q material. Examples of such materials areCOG materials, such as NPO with a high Q value. In addition, thedielectric material should have a relatively high K value, i.e. adielectric constant high enough to achieve the desired capacitance forthe utilized frequencies as the same time as the size of the capacitoris kept at an appropriate size. Typical frequencies used for signaltransfer in this kind of applications, i.e. implantable medical devicessuch as pacemakers, are 402-405 MHz where 110-150 pF is suitablecapacitance values and about 2.45 GHz where 6-12 pF is suitablecapacitance values. In a case where two or more frequencies are used, asuitable capacitance value may be in the range of 15-60 pF for the abovementioned frequency ranges. Another suitable capacitance value range is25-40 pF for the above mentioned frequency ranges. Yet another suitablecapacitance value is about 33 pF. It may be advantageous, from anelectrical and signal standpoint, to use a low K material in an area 111between the capacitor element 108 and an outer cylinder 115 of thefeedthrough, which cylinder may be made of metal. K is defined as theratio of the capacitance with a volume of dielectric compared to that ofa vacuum dielectric, thus, K=εd/ε0, where εd is the permittivity of thedielectric and ε0 is the permittivity of free space. Thereby, thecapacitive coupling between the capacitor and the housing 103 can bereduced. Such a low K material may be various mineral/ceramic materialsuch as e.g. alumina (Al2O3), various types of glass, e.g. Pyrex orglass frit seal s or mixtures thereof, and low K alumina/glass compoundsas used in LTCC ceramics for use in high frequency applications.

The first plate 112 is arranged such that on outer side of it facesoutwards from the device 100. Thus, it may under certain circumstancesbe in tissue contact and is made of a bio-compatible material such astitanium, platinum, alumina, etc. The antenna 102 is attached to thefirst plate 112, and second plate 114, is connected to the RF circuit(see FIG. 1). Preferably, the capacitor element 108 is arranged suchthat the shunt capacitance of the capacitor is minimized.

Furthermore, as discussed above, the isolating dielectric material 109and the first and second plates 112 and 114, respectively, of thecapacitor element 108 integrated into the feedthrough housing 104, arearranged such that a hermetic seal is provided. That is, the capacitorbody or capacitor element 108 functions both as a hermetic seal and as agalvanic isolation and, hence, size, cost, and possible interferenceleakage can be reduced.

With reference now to FIGS. 2 and 3, an embodiment of the feedtroughincluding a capacitor according to the present invention will bedescribed in detail. Like or similar parts having like or similarfunction shown in FIGS. 1 and 2, respectively, are denoted with the samereference numerals. The feedthrough includes a capacitor element 208 anda feedthrough housing 204. As described above, the capacitor body orcapacitor element 208 functions both as a hermetic seal and galvanicisolation and, hence, size, cost, and possible interference leakage canbe reduced.

The antenna 102 is attached to at least one first capacitor plate 212,or anode. At least one second capacitor plate 214, or cathode, isconnected to the RF circuit (not shown in FIG. 2, see FIG. 1).Preferably, the at least one first capacitor plate 212 and the at leastone second capacitor plate 214 are arranged in the feedthrough housing204 such that the feedthrough housing 204 together with the first andsecond plates 212 and 214, respectively, defines an inner cavity 209. Inthis embodiment, the feedthrough housing 204 has a circularcross-section in a plane perpendicular to the plane of the cross-sectionshown in FIG. 2. The first and second plate 212 and 214, respectively,have a circular shape in the plane perpendicular to the plane of thecross-section shown in FIG. 2, and, thus, a cylindrical cavity 209 isformed by the housing 204 and the first and second plates 212 and 214,respectively.

In FIG. 3, the housing 204 and the first capacitor plate 212, which alsois an outer plate with respect to the casing or housing 103, are shownin a top perspective view. A lower part of the antenna 102 is alsoshown.

Furthermore, the first capacitor plate 212, or the first anode, isinterconnected to a number of intermediate anode plates 212 a-212 d,which in this embodiment is four. The intermediate anode plates 212a-212 d are arranged within the cavity 209. In the same manner, asillustrated, the second capacitor plate 214, or the second cathode, isinterconnected to a number of intermediate cathode plates 214 a-214 d,which in this embodiment is four. The intermediate cathode plates 214a-214 d are also arranged within the cavity 209. Of course, as theskilled man realizes, the number of intermediate plates can be varied inaccordance with, for example, requirements regarding size or in order totune the capacitance of the capacitor element 208.

Intermediate anode plates 212 a-212 d and intermediate cathode plates214 a-214 d are arranged in an alternating manner. The intermediateplates 212 a-212 d, and 214 a-214 d are arranged such they aresubstantially parallel with each other, respectively. In addition, theplates 212, 214, 212 a-212 d, and 214 a-214 d are substantiallycircular, in the plane perpendicular to the plane of the cross-sectionshown in FIG. 2, and are arranged coaxially such that they form astack-like configuration. Adjacent plates are separated with gaps d1d9,which in this embodiment are substantially equal i.e.d1=d2=d3=d4=d5=d6=d7=d8=d9. These gaps d1-d9 may be changed in order totune the capacitance of the capacitor element 208.

The inner cavity 209 defined by the feedthrough housing 204 and firstand second plates 212 and 214, respectively, and including theintermediate plates 212 a-212 d and 214 a-214 d is filled with anisolating dielectric material in accordance with the discussion abovesuch that the feedthrough housing 204, the capacitor plates and theisolating dielectric material forms a galvanic isolation and a hermeticseal.

The anode plates 212, 212 a-212 d are interconnected with each other bymeans of wires or leads 220 a and 220 b, which are arranged in via holes222 arranged in the cathode plates 214 a-214 d such that the wires 220 aand 220 b are isolated from the plates. The cathode plates 214, 214a-214 d are in a corresponding way interconnected with each other bymeans of a wire 224 arranged in via holes 226 in the anode plates 212a-212 d. As can be seen from FIG. 2, the capacitor plates 212, 214, 212a-212 d, and 214 a-214 d according to this embodiment have, in a planeperpendicular to the direction of the wires or leads 220 a and 220 b, asubstantially circular shape, as mentioned above. However, as theskilled man within the art realizes, the size and shape of thefeedthrough housing 204 may be another than circular, for examplesquarelike, rectangular or octagonal. Thus, the size and shape of theplates can also be changed, for example, the shape in the planeperpendicular to the direction of the wires or leads 220 a and 220 b maybe substantially octagonal or square. In addition, the gaps d1-d9between adjacent plates can vary. As an example, the gaps d1, d3, d5,d7, and d9 can be longer than the gaps d2, d4, d6, and d8, or in otherwords, d1=d3=d5=d7=d9>d2=d4=d6=d8.

As discussed above, the capacitor element 208 is preferably dimensionedto withstand a voltage exceeding 100 V, and, more preferably, towithstand a voltage in the range of 75-1000 V. Furthermore, thecapacitor element 208 is preferably arranged such that the shuntcapacitance of the capacitor is minimized.

With reference now to FIGS. 4-7, another embodiment of the feedtroughincluding a capacitor according to the present invention will bedescribed in detail. Like or similar parts having like or similarfunction shown in FIGS. 1 and 2, respectively, are denoted with the samereference numerals. The feedthrough includes a capacitor element 308 anda feedthrough housing 304. As described above, the capacitor body orcapacitor element 308 functions both as a hermetic seal and galvanicisolation and, hence, size, cost, and possible interference leakage canbe reduced.

The antenna 102 is attached to a first connecting element 312. A secondconnecting element 314 is connected to the RF circuit (se FIG. 1). Inthis embodiment, the feedthrough housing 304 has a circularcross-section in a plane perpendicular to the plane of the cross-sectionshown in FIG. 4. The first and second connecting element 312 and 314,respectively, has a circular shape in the plane perpendicular to theplane of the cross-section shown in first and second connecting element312 and 314, respectively. FIG. 4, and, thus, a cylindrical cavity 309is formed by the housing 304 and the

In FIG. 5, the housing 304 and the first connecting element 312 areshown in a top perspective view. A lower part of the antenna 102 is alsoshown.

Furthermore, the first connecting element 312 is interconnected to atleast one first capacitor plate 312 a-312 d, which in this embodiment isfour. The capacitor plates 312 a-312 d are arranged within the cavity309. In this embodiment, this first set of plates 312 a-312 d functionas anode plates. In the same manner, as illustrated, second connectingelement 314 is interconnected to a number of at least one secondcapacitor plate 314 a-314 d, which in this embodiment is four. Thesecond set of capacitor plates 314 a-314 d are also arranged within thecavity 309. In this embodiment, this second set of plates 314 a-314 dfunction as cathode plates. Of course, as the skilled man realizes, thenumber of capacitor plates can be varied in accordance with, forexample, requirements regarding size or in order to tune the capacitanceof the capacitor element 308.

Anode plates 312 a-312 d and cathode plates 314 a-314 d are arranged inan alternating manner substantially parallel with each other. The anodeplates 312 a-312 d are attached to the first connecting element 312 suchthat they are substantially perpendicular to the first connectingelement 312. Similarly, the cathode plates 314 a-314 d are attached tothe second connecting element 314 such that they are substantiallyperpendicular to second connecting element 314. In this embodiment, thecapacitor plates 312 a-312 d and 314-314 d are substantiallyrectangular.

In FIG. 6 a cross-sectional view in a plane parallel with the line A-Ain FIG. 4 is illustrated. As in can be seen in FIG. 6, the widths ofadjacent plates differ in this embodiment such that they are graduallybecoming wider in order to adapt to the circular shape of thefeedthrough housing 304. The lengths of the plates are substantiallyequal. An alternative embodiment of the present invention is shown inFIG. 7, where the capacitor plates 312 a-312 d and 314 a-314 d have asubstantially equal widths. Adjacent plates are separated with gapsd10-d16, which in these embodiments are substantially equal i.e.d10=d11=d12=d13=d14=d15=d16 . These gaps d10-d16 may be changed in orderto tune the capacitance of the capacitor element 308.

The inner cavity 309 defined by the feedthrough housing 304 andincluding the intermediate plates 312 a-312 d and 314 a-314 d is filledwith an isolating dielectric material in accordance with the discussionabove such that the feedthrough housing 304, the capacitor plates andthe isolating dielectric material forms a galvanic isolation and ahermetic seal.

As can be seen from FIGS. 4-7, the capacitor plates 312 a-312 d, and 314a-314 d according to this embodiment have a substantially rectangularshape, see in particular FIGS. 4 and 6. However, as the skilled manwithin the art realizes, the size and shape of the feedthrough housing304 can be changed and, hence, the size and shape of the plates, forexample, the shape of the intermediate plates may be substantiallyoctagonal or square. In addition, the distances d10-d16 between adjacentplates can vary. As an example, the distances d10, d12, d14, and d16 canbe longer than the distances d11, d13, d15, or in other words,d10=d12=d14=d16>d11=d13=d15.

As discussed above, the capacitor element 308 is preferably dimensionedto withstand a voltage exceeding 100 V, and, more preferably, towithstand a voltage in the range of 75-1000 V. Furthermore, thecapacitor element 308 is preferably arranged such that the shuntcapacitance of the capacitor is minimized.

With reference now to FIGS. 8 and 9, another embodiment of thefeedtrough including a capacitor according to the present invention willbe described. Like or similar parts having like or similar functionshown in FIGS. 1 and 2, respectively, are denoted with the samereference numerals. The feedthrough includes a capacitor element 408 anda feedthrough housing 404. As described above, the capacitor body orcapacitor element 408 functions both as a hermetic seal and galvanicisolation and, hence, size, cost, and possible interference leakage canbe reduced.

The antenna 102 is attached to a first connecting element 412. A secondconnecting element 414 is connected to the RF circuit (se FIG. 1).Preferably, the first connecting element 412 and the second connectingelement 414 are arranged in the feedthrough housing 404 such that aninner cavity 409 is defined. In this embodiment, the feedthrough housing404 has a circular cross-section in a plane parallel with the line A-Ain FIG. 8. The first and second connecting elements 412 and 414,respectively, have a circular shape in the plane perpendicular to theplane parallel with the line A-A in FIG. 8, and, thus, a cylindricalcavity 409 is formed by the housing 404 and the first and secondconnecting elements 412 and 414, respectively.

Furthermore, the first connecting element 412 is interconnected to atleast one first capacitor plate 412 a-412 b, which in this embodiment istwo. The capacitor plates 412 a-412 b are arranged within the cavity409. According to this embodiment, the at least one first capacitorplate 412 a-412 b function as anode plates. In the same manner, asillustrated, the second connecting element 414 is interconnected to atleast one second capacitor plate 414 a-414 b, which in this embodimentis two. The capacitor plates 414 a-414 b are also arranged within thecavity 409. In this embodiment, the at least one second capacitor plate41 a-414 b function as cathode plates. Of course, as the skilled manrealizes, the number of intermediate plates can be varied in accordancewith, for example, requirements regarding size or in order to tune thecapacitance of the capacitor element 408.

Anode plates 412 a-412 b and cathode plates 414 a-414 b are arranged inan alternating manner as substantially concentric cylinders. The anodeplates 412 a-412 b are attached to the first connecting element 412 suchthat they are substantially perpendicular to first connecting element412. Similarly, the cathode plates 414 a-414 b are attached to secondconnecting element 414 such that they are substantially perpendicular tosecond connecting element 414.

In FIG. 9 a cross-sectional view in a plane parallel with the line A-Ain FIG. 8 is illustrated. As in can be seen in FIG. 9, the capacitorplates 412 a-412 b and 414 a-414 b are arranged in a substantiallyconcentric manner.

The inner cavity 409 defined by the feedthrough housing 404 includingthe capacitor plates 412 a-412 b and 414 a-414 b is filled with anisolating dielectric material in accordance with the discussion abovesuch that the feedthrough housing 404, the capacitor plates and theisolating dielectric material forms a galvanic isolation and a hermeticseal.

As discussed above, the capacitor element 408 is preferably dimensionedto withstand a voltage exceeding 100 V, and, more preferably, towithstand a voltage in the range of 75-1000 V. Furthermore, thecapacitor element 408 is preferably arranged such that the shuntcapacitance of the capacitor is minimized.

Turning now to FIG. 10, a further embodiment of the present inventionwill be described. In this embodiment, the implantable device 500 has abalanced antenna, for example, a dipole antenna, including [[a]] firstand second antenna elements 502 a, 502 b, respectively. The antennaelements 502 a, 502 b, are arranged in first and second feedthroughs,respectively, which feedthroughs, in turn, are arranged in ahermetically sealed housing 503 of the implantable device 500. Eachfeedthrough includes a capacitor element 508 a, 508 b and a feedthroughhousing 504 a, 504 b. As described above, each one of the capacitorbodies or capacitor elements 508 a and 508 b functions both as ahermetic seal and galvanic isolation and, hence, size, cost, andpossible interference leakage can be reduced. Furthermore, the capacitorelements 508 a and 508 b are preferably dimensioned to withstand avoltage exceeding 100 V, and, more preferably, to withstand a voltage inthe range of 75-1000 V. In addition, the capacitor elements 508 a and508 b are arranged such that the shunt capacitance of the capacitor isminimized. The capacitor elements 508 a and 508 b may each have a designin accordance with any one of the embodiments discussed herein withreference to FIGS. 1-9.

In yet another embodiment, the balanced antenna, for example, a dipoleantenna, including a first and a second antenna element is arranged in asingle feedthrough. In this case, the feedthrough contains two capacitorelements, one for respective antenna element, separated from each otherwith an electrically isolating element. As described above, each one ofthe capacitor bodies or capacitor elements functions both as a hermeticseal and galvanic isolation and, hence, size, cost, and possibleinterference leakage can be reduced. Furthermore, the capacitor elementsare preferably dimensioned to withstand a voltage exceeding 100 V, and,more preferably, to withstand a voltage in the range of 75-1000 V.Preferably, the capacitor elements 508 a and 508 b are arranged suchthat the shunt capacitance of the capacitor is minimized. The capacitorelements may each have a design in accordance with any one of theembodiments discussed herein with reference to FIGS. 1-9.

According to still another embodiment, the antenna is arranged forcommunication in two frequency bands. For example, the antenna can bearranged for RF-telemetry communication in a first frequency band at 400MHz and a second frequency band at 2.45 GHz, wherein the first band isused for communication of data such as various operating parameters andphysiological data and the second band is used for wake-up signals. Theantenna is located through an antenna feedhtrough according to thepresent invention, for example, the embodiments shown in FIGS. 2-7. Itshould be noted that the housing effectively is a part of the antennaand affects the radiation properties of the antenna. The housing isfurther in contact with the tissue. Preferably, the feedthrough orcapacitor is dimensioned to constitute a part of the antenna matching atthe first frequency band and the second frequency band, respectively.

Although an exemplary embodiment of the present invention has been shownand described, it will be apparent to those having ordinary skill in theart that a number of changes, modifications, or alterations to theinventions as described herein may be made. Thus, it is to be understoodthat the above description of the invention and the accompanyingdrawings is to be regarded as a non-limiting example thereof and thatthe scope of protection is defined by the appended patent claims.

1-11. (canceled)
 12. An implantable medical device comprising: ahermetically sealed housing configured for implantation in a subject; anRF telemetry antenna carried by said housing; an RF telemetry circuitcomprising an RF transmitter and receiver connected to said RF antennavia a conductive path; a control circuit connected to said RF telemetrycircuit that operates said RF telemetry circuit to transmit and receivesignals via said RF antenna; at least one of said RF telemetry circuitand said control circuit comprising an electrical component that issusceptible to damage or operational modification due to interactionwith a voltage pulse having a voltage amplitude; and a feedthrough insaid hermetically sealed housing for said conductive path, saidfeedthrough comprising a feedthrough housing and a capacitor element insaid feedthrough housing, said capacitor element being connected inseries between said RF telemetry circuit and said RF antenna, and saidcapacitor element comprising a first capacitor plate configurationconnected to said RF antenna and a second capacitor plate configurationconnected to said RF telemetry circuit, said capacitor element beingdimensioned to withstand said voltage amplitude of said pulse.
 13. Animplantable medical device as claimed in claim 12 wherein said firstcapacitor plate configuration comprises a first set of capacitor platesinteracted with each other and wherein said second capacitor plateconfiguration comprises a second set of capacitor plates connected witheach other, the respective plates in said first set alternating withrespective plates in said second set with adjacent plates beingseparated by an isolating dielectric material.
 14. An implantablemedical device as claimed in claim 13 wherein said feedthrough housinghas a substantially cylindrical shape and wherein the respective platesof said first set and the respective plates of said second set aresubstantially circular, and are arranged substantially coaxially in saidfeedthrough housing.
 15. An implantable medical device as claimed inclaim 14 wherein each of said first set of capacitor plates and saidsecond set of capacitor plates comprises end plates with intermediateplates therebetween, each of said intermediate plates having a via holetherein, with all capacitor plates in said first set being electricallyconnected with each other by first conductors that proceed through therespective via holes of the intermediate plates of the second set, andall capacitor plates in said second set being electrically connectedwith each other by second conductors that proceed through the respectivevia holes in the intermediate plates of the first set.
 16. Animplantable medical device as claimed in claim 13 comprising a firstconnecting element connected to said RF antenna and a second connectingelement connected to said RF telemetry circuit, with the plates of saidfirst set being connected to said first connecting element and saidplates of said second set being connected to said second connectingelement, said plates of said first set being substantially perpendicularto said first connecting element and said plates of said second setbeing substantially perpendicular to said second connecting element. 17.An implantable medical device as claimed in claim 16 wherein saidfeedthrough housing has a substantially cylindrical shape, and whereinthe respective plates of each of said first and second sets of capacitorplates are substantially rectangular, each plate in each of said firstand second sets having a width substantially equal to an inner width ofa longitudinal cross-section of said substantially cylindricalfeedthrough housing.
 18. An implantable medical device as claimed inclaim 16 wherein the respective plates of said first and second sets arearranged in substantially concentric cylinders.
 19. An implantablemedical device as claimed in claim 13 wherein the respective plates ofsaid first and second sets are arranged with substantially equaldistances between each other.
 20. An implantable medical device asclaimed in claim 12 wherein said capacitor element forms a matchingelement for said RF antenna.
 21. An implantable medical device asclaimed in claim 12 wherein said first capacitor plate configurationfaces outwardly relative to said hermetically sealed housing, and iscomprised of a bio-compatible material.
 22. An implantable medicaldevice as claimed in claim 12 wherein said capacitor element isdimensioned to withstand a voltage, as said voltage amplitude, exceeding100 V.